After two previous generations of my Solar Power Supply receiving positive feedback on here and YouTube, I thought it would be time to share with you my third generation design.

Much like the previous version, this design improves from the second with a higher capacity battery bank, a more efficient charge controller, better electrical safety in terms of fuse implementation, more outputs and digital displays that show you just how much power is being generated and consumed.

So whether your after a solar power station yourself or are just interested in what's new this time around please read on...

Step 1: What Do You Need Your System to Do?

The first thing to plan is to work out what you will be wanting to power from your system, as mentioned in my previous Instructable, the whole of your house would be nice but seriously expensive and definately not portable. My system will only power small items such as an LCD TV, a couple of 12V energy efficient lightbulbs, a free-to-air receiver, a CD player and radio and to charge mobile phones and other miscellaneous items.

With your power intentions in mind it's important to now figure out the prices for each of the components, I wanted the best of the best so I settled for a top of the range PS-30M 30 Amp Morningstar Charge contoller from Sunstore.co.uk at £198.00 or $315. http://www.sunstore.co.uk/Morningstar-Prostar-30M-Solar-Charge-Controller-with-LCD-Display.html
This charge controller uses Pulse Width Modulation (PWM) to float charge the batteries once fully charged to maintain them whilst incorporating an LCD display to show the battery voltage and solar input current.
For the batteries I went for two Trojan T-105's, being six volts a piece to total 12 volts at 225Ah, this meant that the storage capacity of this bank would be huge, enough to power high drain devices for many hours.
http://www.ebay.co.uk/itm/TROJAN-T105-BATTERY-/130296299020?pt=UK_Lifting_Moving_Equipment&hash=item1e5643be0c

With my two previous generations I used Maplin Electronics and Ebay to source all of my components but this time money wasn't as much as an object so I ended up splashing the cash on a multitude of sites.

The main items to power from the system are then used to calculate just how much power is needed and generated. The LCD TV and receiver draw 2.2 Amps DC on 12 volt, energy efficient lighting draws just under 1 Amp for a 12 watt bulb whilst the phone/GPS chargers draw very little power. Using the TV for say, 3 hours a day max would equal 6.6Ah consumed, lighting used for 4-5 hours a night would consume roughly 4Ah while all the charging of portable devices would be around 2Ah while pumps for air-beds wouldnt run for long so maybe only consuming around 1Ah, totalling 13.6Ah. Deep Cycle batteries shouldn't be discharged below 50% of their rated capacity, the smaller the discharge cycle, the longer the battery will last, therefore a battery of 30Ah would suffice. The UK receives on average 6 hours of sunlight per day during summer, which is the time of year we go camping, the main reason for building this system, therefore replacing 13.6Ah into a battery would take a 50W solar panel roughly 5 hours to recharge.

(Watts = Voltage x Amps)
(Average solar panel voltage at max power = 17 Volts)
(50 watts/17 volts = 2.94 Amps)

It's easier to draw power from a battery than to replace, requiring usually 10% more power to recharge than what was consumed, therefore:
(14Ah / 2.94 Amps = 4.76 hours of direct sunlight)
In a real world situation this will never happen due to too many different factors such as;
Solar panel shading,
Overcast conditions,
Battery temperature,
Size of wiring,
Other losses.

Therefore it's safer to use a larger battery bank, where power can be used up repeatedly if weather conditions the day after aren't suitable for efficient solar charging to completely recharge the battery. My 225 amp hours is way overkill but it's better to have more power than required.

I already had my solar panels from my previous solar power supplies consisting of two AKT 80 Watt solar panels, one BP 80 Watt solar panel and four BP 12 Watt panels totalling a theoretical 290 watts. All of my panels were sourced from eBay over the years.

Step 2: Plan What You Want...

The second step is to plan out what you want your final product to look like. I went through a number of different designs of which I drew up in Microsoft Word of all programs, this really helps you to see just what components will go where and helps to understand any design aspects that won't work.

In the previous versions I used blue LED volt and ammeters whereas this time I wanted a more useful way to show me how much power is being produced and consumed, therefore I ended up purchasing two Turnigy Watt meters, most commonly used for model airplane enthusiasts. These intelligent meters display voltage, amperage, watt-hours, amp-hours, minimum voltage and max amperage consumed and are perfect for use in an off-grid solar power system. I bought two from eBay at £30 a piece and will look great in my system. Using these I can monitor how many volts the solar array is producing aswell as how many watts and amp-hours per day, whilst the other meter shows me how many watts I'm using and have used since the meter was reset.

After many possible versions with components mounted in separate locations, external and internal battery banks and wider and slimmer designs for example, I finally chose the version with a sloped front, a vertically mounted charge controller and separate battery bank for ease of transportation.

I will be reusing the solar panels, Sony car radio, UK mains double gang faceplate, thermostat for the cooling fan and 600 watt mains inverter. With the addition of another cigarette lighter 12 volt output this version of solar supply will have three accessory sockets.

Step 3: Start Building...

The first step was to build the external battery box. 12mm thick MDF (Medium Density Fibreboard) was used for all of the construction and with the Trojan batteries totalling 56 Kilograms, plenty of bracing, heavy duty castors and handles were required in order to move the bank around.

The dimensions were measured up and drawn on a large sheet of MDF, were then cut out and constructed as shown in the images, the more bracing with pine wood the better.

So far so easy...

Step 4: The Main Unit...

Once the battery bank was constructed it was time to build the main unit. As before, a large sheet of MDF was laid out on the floor and the dimensions planned in Microsoft Word were sketched out on the sheet before being cut out in the garage with a wood hacksaw.

It's easiest to cut the longest straight lines first on the workbench, allowing the large piece of wood to be broken down into smaller more easily manageable pieces. Using a hacksaw was the easiest way of doing this although it meant tidying up the edges of the wood after cutting with some sandpaper. It could also have been done using a jigsaw, a lot easier and possible quicker but your lines won't be as straight.

Once all of the panels are cut-out its a case of matching the locations on your diagram and making sure that they're in the right place and are the right size. Once sure, use thicker pieces of wood, some 20mm by 20mm square of pinewood to use as the skeleton for the unit, holding it all together, using 30mm wood screws and a drill to make pilot holes this took no time.

Once the main wooden construction was complete it was time to mount all of the electronics. I initially started with the sockets on the front panel as they're the easiest to mount and wire up, including a two socket UK mains wall socket and three car accessory cigarette lighter sockets, the most efficient way to power devices, directly on 12 volt.

The next things I mounted were the switches, radio, charge controller and meters. The meters as supplied by Turnigy are enclosed in a plastic housing that is easily removed by taking out four little screws. The bare-bone meter is quite compact and is easier to mount in your own enclosure as all you need is a clear rectangular plastic window. The meter LCD's are soldered directly to the board meaning it is very good for incorporating into your own projects as there's no messing around with zebra strips contacting the pcb to the lcd with the products housing.

I used three millimetre plexiglass sourced from eBay for the meter windows. this was cut using a knife to scortch the plastic a number of times before snapping the piece off. This was mounted to the front panel with plenty of hotmelt glue and will not be budging from the case anytime soon.

The switches used this time are of a chrome metallic type. They are all double pole switches which allows them to be very handy for almost any project whilst the colourful LED ring is illuminated with 12 volts DC. I will go into the wiring diagram later on in this Instructable.

The charge controller is simply bolted onto the back panel of the unit with four 1/2 inch bolts, plenty of support is needed here as excluding the batteries, this component is the most expensive on this particular project.

The back of the unit is home to plenty of ports, eight in/outputs for the radio including 4x speaker outs, 2 pre-outs, 1 microphone in for the handsfree feature and 1 sub out for a subwoofer.

Step 5: Wire It All Up!

Once all of the external components are mounted exactly as you want them it's time to wire all of them up, and this is the long difficult bit, lets start initially with the batteries.

Power leaves the batteries in my case through a 50 amp car audio fuse which is the safety between the bank and the main unit itself. It would be pointless simply fusing the system in the main unit itself as if a short developed in the cable to the external battery bank, there could easily be a fire. The cable from the batteries is high grade multi-strand wire rated at 4 AWG (American Wire Guage), allowing the system to have a high capacity for discharge with cables allowing 50 amps to flow with ease, meaning a theoretical 600 watts may be drawn from the batteries safely.

Having the batteries constantly connected to the main unit would be a bit silly so therefore I used a heavy duty Anderson Powerpole connector that is rated also at 50 Amp which allows a quick disconnect to be able to transport the system to wherever it's needed, much easier than all the components and batteries at once which would be near enough impossible to lift using one person.

These cables enter the main unit at the back and go straight to an eight way fuse block which adds more safety to the system again, with the initial fuse in here being rated at 40 Amp, this is still alot of current capacity that can be used. Power then goes through a heavy duty car-style relay rated at 40 Amp which is used to totally disconnect all components through a single power switch, except from the charge controller that needs to be connected to the battery all of the time through a 30 Amp fuse and the car headunits constant power cable which is needed for the radio to retain all of its settings and memory, this time through a 15 Amp blade fuse.

Power is then fed to all parts that need it, the meters, the switches, the relays, radio, sockets, LED's and cooling fans. The eight fuses are as follows: one 40A as the main, three 10A fuses (one for each cigarette output), one 30A for the charge controller, one 15A for the solar input, one 15A for the radio and one 5A for the meters, fan, LED's and relays as they don't draw much power combined. The power inverter has its own fuses so doesn't have it's own fuse, it's still key that it shares the main power fuse for safety though.

There is plenty of wires in this solar supply and with the radio and inverter being powerful items, air circulation is a necessity and is provided by a 12cm green illuminated fan at the back of the unit. This fan is activated when the internal air temperature gets around 28 degrees Celsius and is activated by the battery powered central heating thermostat that was used in my last solar power box. It doesn't require powereing from the main system and with it drawing very little power, the batteries last a LONG time.

The Solar panel input is through the use of a Tamiya style remote controlled car battery pack connector which allows me to quickly and easily disconnect the solar array. This input is fused with a 15 Amp fuse before entering the charge controller, it's better to be safe than sorry.

One thing to note is that the Turnigy meters can be powered from the source they are measuring but also an external power supply so that they can measure down to 0.1 volts. The solar input meter must use a relay to disconnect the voltage measurement lead from the solar input when the meters are turned off, otherwise when the sun rises the voltage slowly climbs which illuminates the meter but is not instantly enough for the meter to boot up. The external power input is used via the use of a 12 volt DC to 12 volt DC converter which allows the meter to be used even when the sun goes down to provide statistics for energy produced during the day but also provide safety to not bridge the gap over the charge controller.

Please refer to the brief wiring diagram in the next step to see how all of the components were connected...

Step 6: Circuit Diagram...

This step includes a brief diagram to the wiring arrangement of my system, note the different thickness of power lines, the thicker cable carries more current than the thinner.

Step 7: Finishing Touches...

Once the majority of the project is complete it is time to make it look nice using labels. In my previous Instructable I showed you how I design my labels in Microsoft Word, print them out, cover them in sellotape then apply double sided sticky tape, this time I went the easier route of using my Brother label printer. While you can't include pictures and colour into your labels this way, it's much quicker and easier and I think looks better. Simply type your own label, with or without borders, styles or symbols, hit print, then cut the printed label to the correct size and stick on.

I purchased mine from, yes you guessed it, Maplin Electronics for £14.99 and is still available at that price with two tape cartridges at: (http://www.maplin.co.uk/p-touch-pt-1005bts-labelling-machine-with-2-free-tapes-340863)

Step 8: Improvements/Alterations

Under heavy discharge the battery voltage displayed on the meters and charge controllers LCD screen sagged a little by upto 0.3 volts, which is alot in terms of lead acid battery voltage monitoring so something had to be done about it. The easiest way to fix this issue was using a separate cable from the battery terminals and use them as the voltage sense source. Current isn't drawn by the system through these wires so their voltage doesn't sag under load.

I used two core mains cable, both wires fused in the battery box with a three amp fuse each before the cable terminates at the main unit through a locking-multipole connector available from Maplin Electronics at (http://www.maplin.co.uk/locking-multi-pole-line-sockets-43121). This allows me to easily disconnect the unit from the batteries easily, but also allows me to have a good reference voltage source to judge how charged my batteries are.

Another improvement I implemented was the addition of two bright white LED's, one for each meter as the standard blue ones make the displays quite difficult to read. Soldering the leads to the LED's before heatshrinking the whole LED except the lens output end allowed me to get the placement spot on behind the factory blue LED, a spot of Blu-Tac allowed me to position it before covering it in hot-melt glue. Two 1K Ohm resistors supply enough current limiting to the LED's to brightly light the displays to see easily with the eye from quite some distance away.

As in the previous solar box design I added the portable USB hard drive that stores over 20GB of music that I can search through on the Sony MEX-BT3800U headunit and allows the unit to act as a media center. Hard drive activity is indicated by the flashing HDD LED on the front panel just to the left of the meters which is transferred by a light dependant resistor circuit which you can find in my previous Instructable.

Step 9: Useability and Final Thoughts.

My system can provide alot of power once the sun has gone down. With the two Trojan deep cycle batteries I can easily power a 30 watt mains halogen bulb, the radio, a lava lamp and a subwoofer for the radio all night with ease. If these items are left on for around six hours the number of amp hours consumed is around 25Ah, whereas a possible 110Ah is available to consume (half of the batteries capacity). This system is the best one that I have built yet and wish to keep it in operation for years to come and not to upgrade to a better one after a year. The best thing is when I have my items running off of my solar power supply at night and then suddenly residential mains power goes down so everyone else in the neighbourhood is in the dark whereas I'm perfectly fine and quite often don't even notice that utility power has gone offline.

The only possible way I can think to improve on this design is to allow my battery bank and solar array capacity to grow as all of the components in the middle are fine as they are. O.k, maybe a pure sine wave inverter for any picky mains electrical items would be nice, although I've failed to find an appliance or device that won't accept a modified sine wave input.

However your off-grid solar power supply goes I wish you the best of luck with the design and manufacture, but remember, Have Fun!

Step 10: PICTURES!!

Here's a few pictures of my off-grid solar power system, I will hopefully put together a video sometime in the near future when I have time. Well that's all for now, If you have any questions please don't hesitate to ask in the comments below and thank you for reading.